1. Field of the Invention
This invention relates in general to subsea well drilling equipment, and in particular to a tieback system for a subsea well that has a downward facing funnel section and an internal profile for releasably receiving the lower end of a tieback conduit.
2. Description of the Prior Art
In one type of offshore well drilling, a subsea wellhead housing will be located at the sea floor. Casing will be cemented in the well. After installing at least one or more strings of casing, the drilling riser will be removed. A tieback riser will be installed with the tieback connector connecting the tieback riser to the wellhead housing. The tieback riser extends to the surface where a Christmas tree will be eventually installed for production.
In some cases, one drilling rig drills the well and installs casing. The first vessel will install a cap and move from location. At a later date, a production platform will position itself over the well for completion. The production platform will remove the cap and connect the subsea wellhead housing to the production platform by a tieback riser and a tieback connector. The production platform then completes the well.
One type of tieback connector employs a downward facing funnel mounted to the lower end of the tieback conduit. The funnel slides over the wellhead housing. In one type of tieback connector, a locking element such as movable dogs will engage grooves on the exterior. With the locking element on the exterior, full bore access to the wellhead housing is provided. However, this type is fairly large and expensive. Often a number of wells are drilled through a template at the same location. Because of the close spacing of the wellhead housings, the large outer diameter of the funnel and connector can be a problem for clearances.
In another type, the tieback connector latches into interior grooves formed in the bore of the wellhead housing. While this type has a lesser outer diameter than the external connector type, the locking element for the interior normally restricts full bore access to the wellhead. The lack of full bore access has disadvantages in some completion techniques.